The present invention relates to an analog front-end circuit, an electronic instrument, and the like.
In an image sensor such as a CCD or CMOS sensor used for electronic instruments such as an image reader, an analog image signal relating to a document or the like read by the image sensor is converted into a digital image data using an A/D converter. JP-A-2004-297146 discloses technology relating to an analog front-end circuit (image processor) having such an A/D converter.
As a method which controls the offset or the gain of such an analog front-end circuit, an external CPU (firmware which operates on a CPU) may set an offset control value or a gain control value in a register before scanning a document to implement offset control or gain control.
According to this method, since a closed-loop feedback occurs within the image sensor (line sensor), the analog front-end circuit, and the CPU, it takes time to prepare to read a document. Moreover, since firmware which operates on the CPU is required, it is necessary to construct an analysis algorithm or analysis means.